[Python-ideas] Dict joining using + and +=

Chris Angelico rosuav at gmail.com
Fri Mar 1 07:47:07 EST 2019

On Fri, Mar 1, 2019 at 11:00 PM INADA Naoki <songofacandy at gmail.com> wrote:
> I dislike adding more operator overload to builtin types.
> str is not commutative, but it satisfies a in (a+b), and b in (a+b).
> There are no loss.
> In case of dict + dict, it not only sum.  There may be loss value.
>    {"a":1} + {"a":2} = ?
> In case of a.update(b), it's clear that b wins.
> In case of a + b, "which wins" or "exception raised on duplicated key?" is unclear to me.

Picking semantics can be done as part of the PEP discussion, and
needn't be a reason for rejecting the proposal before it's even made.
We have at least one other precedent to consider:

>>> {1} | {1.0}
>>> {1.0} | {1}

I have absolutely no doubt that these kinds of questions will be
thoroughly hashed out (multiple times, even) before the PEP gets to


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